In the solid state electronics industry, a multitude of devices such as integrated circuits (ICs) are typically formed in an active surface of a semiconductor wafer. Such forming includes plating metal on an active surface to establish current paths, contact pads, leads and other features of the devices. A problem is to properly plate on the active surface only and not on a reverse, inactive side or on other surfaces.
Such plating is advantageously accomplished by a process sometimes referred to as high velocity plating. Each wafer is held in a pocket of a vertically oriented holder board which is immersed in a plating bath. The inactive surface of a wafer is sealed off to avoid unwanted wetting, and the wafer is electrically connected to the cathode terminal of a rectifier. A pump and jet assembly is utilized to propel streams of solution primarily onto the active surface of a wafer. Typically, there is a disposed in the solution stream, a metallic grid which is electrically connected to the anode terminal of a rectifier to complete a current path via the grid through the solution stream to the active surface. A continual stream of solution impinging upon the active surface expedites ion exchange and electroplating is thereby enhanced. A problem is to hold a wafer firmly against the pressure of a solution stream. Another problem is to effectively seal around an active surface so solution does not wet, plate and/or corrode other surfaces. A further problem is to achieve good contact to deliver a desired current to an active surface without damaging the wafer.
The inactive surface of a wafer is generally inappropriate for electrical contact because of the desire to keep such surface unwetted and because dielectric layers such as silicon nitride are often present. Consequently, peripheral regions of the active surface are contacted, typically utilizing pointed pins made of a metal which tolerates the usually corrosive environment. A problem is that the pointed pins often damage a wafer under efforts to achieve good contact. Another problem is that the metal pins become parasitically plated and must be cleaned. A further problem is that metals which are inherently good conductors often donate unwanted impurities to plating solutions.
Accordingly, it is desirable to develop new and improved expedients for plating on a surface, especially on an active surface of a semiconductor wafer. Such wafers are easily broken and should be softly coupled to a current source with sealing contacting members without exposing metal surfaces to plating solutions.